Bituminous composition and process for making same



Patented Dec. 28, 1926.

uurrsn STATES WILLIAM P. BENTLEY, 03? DALLAS, TEXAS.

No Drawing.

This invention relates to bituminous composition and process for making same, and more particularly relates to the utilization of natural rock asphalt composed of calcareous or silicious mineral aggregate naturally containing a certain percentage of bitumen, by combing same with a graded non-bituminous mineral aggregate and a predetermined percentage of a bituminous flux.

- Among the objects of the present invention are to provide a product, admirably adapted for use as roadways, foot paths, sidewalks, floor coverings and the like; to produce a product which combines the innate characteristics of stability and waterproofness, common to certain types of natural rock asphalts used per se with additional resistance to Wear and increased stability derived by the increased denseness of this mixture; to provide a product consisting in part of locally available mineral aggregate. thus producing a composition more economically than has been previous practice; to provide a process of combining natural rock asphalt with its bitumen content, with graded non-bituminous mineral aggregate and adding a. heated flux.

Heretoforc," it has been the common practice to use carefully selected and certain rock asphalts, pulverized and fluxed, without the addition of mineral matter, Such products are naturally expensive at any distance from the rock asphalt source as nearly100% oi the material must be transported.

I have found that by the process hereinafter described in detail, I can produce a pavement mixture comprising as low as 30% of the native rock asphalt, in which the inherent stability moisturcproof qualities and resistance to attrition, abrasion and displacement are equal to, if not greater than pavcn'ients constructed of 100% rock asphalt aggregate. This is attributed to the more advantageous grading of the supplemental aggregate which produces a mixture of. corn siderably lower voidage which is, of course, more compact and also more permanent and stable due to the fact that 100% of the aggregate is sharp and angular.

I have further "found that only in instances where the native rock asphalt is low in bitumen content, is it necessary to add more flux than has been the practice in using the rock asphalt in entirety. This is true for the reason that the reduction in voids occa Application filed May 9, 1924.

TBIIITI'IMIINO'U'S COMPOSITION AND PROCESS FOR MAKING SAME.

Serial No. 712,027.

sioned by the addition of graded mineral aggregate .reduces the amount of bitumen necessary'to fill said voids. In cases where it is found necessary to increase the percentage of finally contained bitumen, I have found that this can be done either by the addition of solid or semi-solid asphalt, or by using a flux of the proper consistency, and that by regulating the quantity and viscosity of said added bituminous materials, it is possible to control Within very close limits the penetration of the resulting bitumen content as well as the final percentage of same. For successful results this percentage must be within the range .5% and the penetration within 5 tenths of 1 mm.

Having thus outlined the advantages to be accrued from the present invention, I will now describe one manner in which such a composition adaptable for surfacing concrete roadways, maeadam, brick, gravel or such, having a suitable foundation and subgrade may be prepared.

To a minimum of about 30% by weight of crushed rock asphalt (previously analyzed for bituminous content and granular metric proportions), I may add about of crushed stone or rock or screened gravel in such proportions of each size, as measured by passing through a suitable ring, that a minimum of voids is produced. The voids may be previously determined by testing in any of the Well known void meters, such as a cylinder, cone, or screw meter, and such combinations of the various sizes used which will give the lowest percentage of voids. I prefer to use aggregates of diameter not larger than one-half the depth of the finished pavement.

The non-bituminous mineral aggregate and the crushed rock asphalt (such as Uvalde rock asphalt) may be heated separately, or in combination, in an approved type of cylinder or drum to such a temperature as will readily cause the bitumen in the rock asphalt to' flow and coat the particles of the non-bituminous mineral aggregate. With Uvalde rock asphalt this temperature mav be approximately 300 F.

\Vhen at the proper temperature, the mixture may then be treated as described below. It may also be transferred to a weigh box and thence to a pug mill or other suitable .device' and treated therein as described.

Flux oil of the kind normally used with lUvalde rock asphalt, namely, 19 to 21 Baum gravity mineral oil flux, is sprayed or added by gravity, and the mixture then agitated until the flux has coated all the particles and become thoroughly mixed with the naturally contained bitumen, thus efi'ecting its softening action. For one typeof pavement I have found that 1.5% by weight of the 21 Baum gravity oil in proportion to the amount of rock asphalt used is suiiicient. If so desired, the flux oil may be first combined directly with the rock asphalt and then agitated with the hot mineral aggregate. In cases Where prevlous analyses have shown that the bitumen in the rock asphalt is of a proper consistency for the intended purpose, and it is only necessary to increase the percentage of bitumen, same may be accomplished by adding asphalt of paving consistency rather than flux o1l. Also, it may be feasible to use combinations of flux and asphalt or semi-solid bitumens, and these may be added separately or previously compounded, for instance at a petroleum refinery.

If it is found that in rock asphalt other than Uvalde that there is a deficiency of line aggregate, that is, material passing a ,1 inch circular opening, and that the voids are not relatively as low as in the Uvalde rock asphalts, sand may be added directly to the coarse aggregate or combined with the rock asphalt immediately before heating.

This finished mixture may then be transported to the. site of the work, and spread,

and compressed in the manner usual to pavements of this character. When thoroughly compressed, but while still warm, a protective layer or" finely crushed and :tluxed pure rock asphalt may be spread in thin layers, sayup to one-half inch, and again rolled. This will render the pavement more waterproof, and will also-protect the larger particles of mineral aggregate from impact occasioned by assing over of heavily loaded vehicles. Vhen Uvalde rock asphalt is used, the protective coat is not usually necessary as this material is well known to be more moistureproof than any other bitumiimaeii heated non-bituminous graded mineral aggregate suflicient crushed bitumen containing rock also heated to fill the voids thereof after compression, adding to the mixture a flux in liquid condition in suiiicient quantity to coat the mineral aggregate and fill the remaining voids in the mixture, whereby to produce a paving mixture in which the mineral aggregate predominates in volume.

2. A paving composition of the bituminous-concrete type comprising graded mineral aggregate mixed with sufficient crushed bitumen containing rock to fill the voids thereof after compression and a hydrocarbon flux in suflicient quantity to coat said stone and fill the remaining voids in the mixture, the bitumen containing rock serving as a mortar constituent, the mineral aggregate predominating by volume.

3. A pavement of the bituminous-concrete type, the constituent ingredients of which comprise in admixture, graded mineral aggregate, bitumen containing rock in sufiicient quantity relative to the mineral aggregate to fill the voids thereof and bituminous flux in suflicient quantity to coat the mineral aggregate and fill the voids in the mixture,

the mineral aggregate predominating on a volume basis relative to said other constituent ingredients.

a. A pavement of the bituminous-concrete type, the constituent ingredients of which comprise in admixture, graded mineral aggregate, bitumen containing rock in sufiicient quantity relative to the mineral aggregate to'fill the voids thereof and bituminous flux in sufiicient quantity to coat the mineral aggregate and fill the voids in the -mixture, the mineral aggregate predominating on a volume basis relative to said other constituent ingredients, and a surface coating comprising pulverized bitumen containing rock.

WILLIAM P. BENTLEY. 

